<!DOCTYPE html>
<html>
<head>
    <meta charset="utf-8" />
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <title>Page Title</title>
    <meta name="viewport" content="width=device-width, initial-scale=1">
    <link rel="stylesheet" type="text/css" media="screen" href="main.css" />
    <script src="main.js"></script>
    <style>
    /* h1 {
        color:red;
    } */
    .a{
        color:blue;
        font-size:14px;
    }
    #abc {
        text-align: center;
    }
    </style>
</head>
<body>
    <h1 class="a">Hello world!!</h1>
    <p class="a"> 这是段落</p>
    <p id="abc">这是特定的段落</p>
</body>
</html>